1. Field of the Invention
This invention relates to an adjustable motor vehicle suspension comprising an adjustable suspension unit and a control system therefor.
2. Disclosure Information
Adjustable suspension units, and particularly adjustable suspension units with adjustable damping capability have been the subject of numerous patents. For example, U.S. Pat. No. 3,603,612 discloses an adjustable shock absorber in which an electronic control valve is operable to change the damping capability of the unit as a function of vehicle speed.
Adjustable shock absorbers have been employed with a variety of control schemes. An example of one such control scheme is disclosed in U.S. Pat. No. 4,333,668 in which damping is controlled as a function, inter alia, as a function of body roll. For the purposes of this document, the term "body roll" refers to a potentially objectionable tilting or leaning of an automobile body from its normal ride attitude during turning, stopping, braking, or other maneuvers.
U.S. Pat. No. 4,564,215 discloses a control system in which a bistable suspension unit is switchable from a soft state to a hard state.
U.S. Pat. No. 4,589,676 discloses a control system which senses road undulations and changes the damping characteristics of the suspension unit accordingly. This device, as well as the previously described devices, includes hydraulic means for damping road-induced vibrations. Although such means may be satisfactory under certain conditions, hydraulic suspension units are generally incapable of achieving fast response in the 10 to 15 Hz. frequency regime which characterizes the vertical suspension motion of many modern motor vehicles.
U.S. Pat. Nos. 3,913,938; 3,992,039; 4,364,574; 4,453,725; and 4,591,185 each disclose a type of suspension system including vehicle height or level control capability. Each of these devices is either hydraulically or pneumatically actuated and each functions at a steady state to control the height of a vehicle body with respect to the balance of a suspension system. None of these systems is capable of controlling the suspension unit in the manner herein described while the suspension unit is oscillating at the natural frequency of the suspension system, which includes the suspension unit, the wheel and tire assembly, and any other dampers or spring elements.
U.S. Pat. No. 3,606,365 discloses an active suspension system for a vehicle in which the vehicle body is supported by a piston and cylinder arrangement. Oscillations of the body are counteracted by manipulating the volume of fluid on either side of the piston. This system, too, is not capable of high frequency response because of the lag time associated with the various valves and other hydraulic devices included in the system. Such hydraulic devices are generally incapable of accurately controlling a suspension system during a half cycle stroke because of a non-linear relationship between the force the hydraulic damper generates and the input control signals. This non-linearity results from the characteristics of the hydralic valves, from the compressibility of the hydralic fluid, and other factors, and makes it difficult to control damping force independent of damper velocity. Other problems with hydraulic dampers stem from the compressibility of the hydraulic fluid and from the fact that hydraulic dampers cannot easily generate high forces at low damper velocities. Such a capability is desirable for anti-dive, anti-squat, and anti-roll vehicle control. Yet another deficiency in hydraulic dampers resides in the fact that such devices typically exhibit high frictional losses due to hydraulic seals.
Designers have attempted various configurations for sliding friction dampers or shock absorbers. In fact, sliding friction dampers were known at the dawn of the automotive age. For example, U.S. Pat. No. 375,759 discloses a sliding frictoin shock absorber which is adjustable by means of either a wedge or a four bar link mechanism. Other types of sliding friction shock absorbers are shown in U.S. Pat. Nos. 1,671,658; 3,052,458; 3,866,724; and 3,990,542. French Pat. No. 1,143,703 discloses yet another type of sliding friction shock absorber. None of these designs is suitable for integration in an automotive suspension system wherein it is desired to control the damping of the shock absorber depending upon which stroke of the two stroke cycle the damping device, as well as the balance of the suspension in which the damping device is included, happens to be operating in. Each of these aforementioned sliding fricton shock absorbers suffers from a similar deficiency residing in the fact that there is no feedback of the force developed by the device. As a result, wear within the device cannot be accounted for except in a gross sense--i.e., by adjusting the unit when a loss of ride control is noted by the vehicle operator.
It is an object of the present invention to provide an adjustable motor vehicle suspension comprising an adjustable suspension unit and a control system therefor which will permit dynamic adjustment of the damping of the suspension unit depending upon which stroke of a two stroke cycle the suspension unit is operating in.
It is another object of the present invention to provide an adjustable motor vehicle suspension comprising a control system which will allow the vehicle suspension to counteract body roll during cornering, brake dive, and acceleration squat.
It is yet another object of the present invention to provide an adjustable motor vehicle suspension comprising a control system which will counteract vertical oscillations of the vehicle body in response to inputs from the suspension.
It is an advantage of the present suspension that the control system can be used to control sliding friction shock absorbers capable of producing maximum force at a relative suspension velocity of zero (i.e., when the velocity of one part of the suspension unit is zero with suspect to the other part of the same suspension unit.)
It is another advantage of the present suspension that the control system may be employed to control sliding friction shock absorbers or other types of adjustable suspension unit having lower lag time characteristics.
It is yet another advantage of the present invention that a suspension according to the present invention uses the resilient energy of the suspension system to counteract undesired movement of the vehicle body.
It is yet another advantage of the present invention that this suspension may be used to produce high damping force inputs to the vehicle body without requiring power input from a hydraulic pump or other high power absorbing device.
Other features, objects and advantages of the present invention will be discussed and disclosed in this Specification.